Ninety-three years ago yesterday, the Boston police force went on strike, leaving the city unprotected while the state scrambled to find replacements. Governor Calvin Coolidge's declaration of support for the city -- he said that "There is no right to strike against the public safety, anywhere, anytime" -- established his national reputation that ultimately led to the presidency.

Public outrage at labor actions that compromise public safety has historically been a bipartisan affair. Coolidge was a Republican but his actions earned the respect of Democratic President Woodrow Wilson, who hailed his re-election as Massachusetts governor as "a victory for law and order." Nearly 20 years later, President Franklin Roosevelt shared his view that a strike by public employees of any sort is "unthinkable and intolerable."

The impacts of the Chicago teacher strike that began today may not be as immediately obvious as the looting and vandalism that descended on Boston in 1919, but they are just as serious. Research from a large, urban school district found that teacher absenteeism has a negative impact on student learning in math.

But a strike doesn't leave students with substitute teachers -- it leaves them without any school at all. Research on summer learning loss shows that being out of school has a disproportionate effect on low-income students. One recent study found that "while all students lose some ground in mathematics over the summer, low-income students lose more ground in reading, while their higher-income peers may even gain." In other words, the consequence of being out of school is to increase the already unacceptably large achievement gap between low-income students and their affluent peers.

The American labor movement has made important contributions in areas ranging from workplace safety to child labor to employment discrimination. There are good reasons to believe that the public ought to accept higher coal prices resulting from a strike to protect the lives of miners. But the public should not tolerate damage to the education of disadvantaged students resulting from a strike over disagreements about teachers' salaries, benefits, job security, and method of evaluation.

The Chicago Teachers Union's differences with the city over how the public schools ought to be run may well be legitimate. But those battles should be fought in the court of public opinion and ultimately at the ballot box, not through strikes that come largely at the expense of poor children.